Field of the Invention
This invention relates to a method for producing a pigment-organic vehicle product and the product produced thereby.
In the preparation of inks, paints, colored plastics, and the like, it is essential that the pigment be uniformly dispersed in the vehicle. There are many techniques for improving dispersibility of pigments such as adding the pigment in the form of a fine powder generally produced by drying and grinding the presscakes. However, powdered pigments are difficult to redisperse to obtain maximum dispersion.
While pigment presscake disperses more readily in an ink composition than dry pigment powders, nevertheless, due to the low solids content of the aqueous cake generally obtained by conventional processes, dispersion of untreated presscake in inks is not economically feasible because of the low pigment loading. Methods for preparing high solids presscakes from the conventional presscake obtained from a filter press are known to those skilled in the art. Such high solids presscakes allow for high pigment loading and are readily dispersible in inks but are difficult to handle and particularly are not readily pumpable.
Accordingly, the pigment is often "flushed" to transfer the pigment particles from the aqueous phase to a non-polar oil or resin phase. This assists in keeping pigment particles non-agglomerated and easier to dilute for ultimate use in inks or coatings. Flushing has been carried out for many decades by mixing pigment presscake with suitable types and quantities of "vehicles" which may be an oil, or a solution of resin or resins and other additives in a solvent. In the prior art, the transfer was effected by merely kneading the presscake and vehicle together until a major portion of the water has separated. Periodically the flushers have to be tilted to remove water from time to time as it breaks, i.e., becomes freed of pigment which has transferred to the oil phase.
It is a purpose of the instant invention to increase filter press capacity through increased bulk density of the material being filtered and to reduce flushing cycle time by significantly reducing the break phase portion of the flushing cycle.
U.S. Pat. No. 4,230,610, issued Oct. 28, 1980, to Falcione et al, assigned to Calgon Corporation, discloses the use of polyacrylates as dispersants for aqueous magnesium oxide pigment slurries prior to dewatering. The polyacrylate is obtained by neutralizing poly(acrylic acid) to a pH of from about 8 to about 12 with bases such as sodium or ammonium hydroxide. This changes the solubilization process properties of the polyacrylic acid resin from oleophilic to hydrophilic.